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The book is a collection of studies previously presented at a Conference on Parts of Speech (henceforth PoS) held at the University of Amsterdam in 2006. As explicitly stated by the editors in their short introduction, the volume aims at offering a specimen of very different perspectives from which the study of PoS can be approached.

The first article is about ''Word classes in sign languages.'' Since the paper is not addressed to sign languages specialists, the authors, W. Schwager and U. Zeshan, devote the first section to the presentation of some basic features of sign languages and summarise some theoretical issues concerning PoS systems in these particular kinds of natural languages. After assuming the essential equivalence between sign and word (Zeshan 2002), Schwager and Zeshan underline how the topic of identification of PoS in sign languages has been neglected by scholars (with few relevant exceptions, from Supalla and Newport 1978 to Johnston 2001). It is not clear according to which morphological and syntactic regularities PoS should be recognised in sign languages. Thus, in the following section, in order to determine relevant criteria to recognise PoS in sign languages, the authors analyse extensively sets of data from two typologically different languages: German Sign Language and Kata Kolok (the latter being used by a village community in Bali with a high incidence of hereditary deafness). Because of their typological distance, the base for their comparison is the semantic level. Signs from both languages belonging to the same ''concept class'' (Sasse 1993) are compared on the basis of an established set of binary features, which are supposed to be valid cross-linguistically. Then, the comparison can be conducted at a syntactic level and a morphological level as well (at least for languages with a larger array of morphological processes), with the aim of determining to which extent syntactic and morphological criteria can be helpful in word class assignment.

In ''Roots, stems and word classes,'' Ch. Lehmann deals with the levels of categorisation of linguistic signs. Assuming the ascending sequence ROOT > STEM > WORD FORM > PHRASE as representing the levels relevant for the categorization of units with lexical meaning (Table 1, p. 45), his main question is the following: At what rank of such a sequence is the linguistic sign categorised? By using a small sample of roots from six languages (Latin, Spanish, English, German, Mandarin Chinese and Yucatec Maya), Lehmann shows that this question can be answered at the level of a single-language. Languages indeed differ in the degree of autonomy of lexical meaning versus category meaning. For instance, the same concept 'comfort' is coded in different ways in Spanish and Mandarin Chinese: the Spanish stem 'consol-' can only be inflected as a transitive verb, whereas the Mandarin Chinese stem 'anwèi' can be used both as a verb and as an adjective. This means that in languages like Spanish, word class assignment occurs at a lower level of grammatical categorization (see again Table 1) than in languages like Mandarin Chinese. However, such a (primary) categorization follows from a probability calculus: ''what will most probably be the syntactic function of this lexical concept?'' (p.47). Moreover, it is determined by universal cognitive principles among which the so-called time-stability of a concept (Givón 1979; Croft 1991). On the basis of empirical data, Lehmann arranges a scale of categoriality (= category determinacy) for roots and stems of the target languages.

The contribution by W. Bisang (''Precategoriality and syntax-based parts of speech'') is well aligned with Lehmann's perspective and analyses the topic of word class assignment in Late Archaic Chinese (5th-3rd century BC). The aim is to show that precategoriality in the lexicon cannot be a universal feature, although most theoretical approaches take it for granted. Establishing whether or not lexical items (=roots) are precategorial is an empirical issue to be investigated at the level of the single language. Through the analysis of data, Bisang illustrates the extent to which Late Archaic Chinese really has precategorial (i.e. not preclassified) lexical items. Most of them can be assigned to the noun-position as well as to the verb-position without any difference in marking. However in some cases, lexical items show at least a tendency to take either syntactic position, depending on the following stereotypical implicature: CONCRETE OBJECTS > ABSTRACT OBJECTS (where '>' means 'implies stronger N-inference than'). Such a hierarchy can also be given in terms of an animacy hierarchy: 1st/2nd PERSON > PROPER NAMES > HUMAN > NONHUMAN > ABSTRACTS. This means that word class assignment depends on a probabilistic factor (as Lehmann claimed too), which -- in Bisang's perspective -- is linked with stereotypical implicatures that are based on the animacy hierarchy. Beside such pragmatic aspects, the interpretation of lexical items in Late Archaic Chinese is fully established within the syntactic framework of the argument structure construction. Embracing the approach of Construction Grammar (e.g., Goldberg 2005), the author claims the meaning of lexical items to be the result of their own lexical meaning plus the meaning contributed by the construction. To this end, a number of syntactic constructions are tested.

The article by M. Donohue on ''Covert word classes'' examines syntactic categories in Tukang Besi, an Austronesian language of Indonesia. Despite the existence of precategorial roots in Tukang Besi, Donohue shows recognizing word classes to be important, if sometimes difficult. Its usefulness emerges, for instance, when describing affixation strategies (pp. 91-93): e.g. some suffixes show restrictions on the input word class, others do not. The main focus of the discussion is on a particular class of 'property concepts,' which might correspond to adjectives in other languages. In Tukang Besi, this is a covert word class in the sense that it cannot be defined based on particular specific morpho-syntactic properties. Nevertheless there is enough internal semantic consistency -- the lexemes denote property concepts -- to suggest that they be treated as a separate word class.

The fluid status of adjectives across languages is the topic of another contribution: ''Pragmatic factors in the development of a switch-adjective language'' by Y. Koloskova and T. Ohori. The case study is drawn from the Miyako-Hirara dialect of Ryukyuan (a sister language of Japanese), which is characterized by the presence of the so-called 'switch-adjective' (Wetzer 1996:80), i.e. it employs both 'nouny' and 'verby' morpho-syntactic strategies for its adjectival roots. Both the strategies are used to encode adjectives in the predicative function (= predicative adjectives). The paper aims at revealing which factors determine the choice of either strategy and argues that in Miyako-Hirara this depends on pragmatic factors, i.e. the informational status of the predicate. By discussing a range of exemplifications, the authors claim that predicative adjectives are marked by 'nouny' morphological and distributional patterns when the property denoted by the adjective is new to the hearer (focus domain). By contrast, 'verby' morphological and distributional patterns encode a property which is supposed to be familiar to the hearer (presupposition). From a typological point of view such a mixed pattern is not common.

D. Gil's paper discusses ''The acquisition of syntactic categories in Jakarta Indonesian.'' After giving a short overview of the different theories of syntactic categories in the linguistic literature, Gil explains the criteria that led him to the adoption of one of them, i.e. the one ''involving a relation of domination not based on set inclusion'' (p. 137). A significant part of the article (Section 2) is devoted to the presentation of such a theory -- which is syntactic and formal, being partially in line with the description of Chomsky (1970). Of course, Gil's adoption of an empirical method is a strong difference. The fundamental prediction that simpler syntactic categories (higher in the Syntactic Category Tree) be existentially prior to more complex ones (lower on the Syntactic Category Tree) is tested in the domain of ontogeny, i.e. first language acquisition, by using a large corpus of Jakarta Indonesian.

In their short paper ''Possible phonological cues in categorial acquisition,'' J. Don and M. Erkelens present the result of an experiment in which adult native speaker of Dutch were asked to categorize a certain number of stems as nouns or verbs. The aim was to determine whether word categories can be assigned solely on the basis of phonological information aside from semantic and syntactic properties of the word. Phonological cues identified by Trommelen (1989) are used in order to sketch out a sort of phonological identikit for word classes. Since the experiment seems to confirm phonological cues as helpful elements in the discrimination of nouns and verbs (as others previously did for English), according to the authors this would support the claim that this strategy is also plausible in children's word acquisition.

Another short article, ''Lexical semantic constraints on noun roots and noun borrowability,'' by L. Nichols, deals with matters of language contact, taking into account the peculiar case of Zuni, an isolate language spoken in New Mexico. Nichols shows that noun (= noun roots, not complex nouns) borrowing is limited into languages -- like Zuni -- in which particular constraints limit the lexical semantic content of noun roots. Borrowed nouns, indeed, must enter into the semantic categories of nouns permitted by constraints on the native root lexicon that limit noun roots to natural kinds (e.g. animals, plants, people, etc.). This case is evidence of the fact that crosslinguistically noun borrowing may be subject to restrictions.

The last three papers all share a link with the so-called Amsterdam model of PoS (whose foundations are in Hengeveld 1992). Starting from the assumption of this model, in his article ''Degree words, intensification, and word class distinctions in Romance languages,'' V. Salazar-García displays how some of its problematic aspects may be solved by extending the fundamental basis of the theory to another domain, that of linguistic variation. In order to do so, it is necessary to think flexible and rigid grammatical strategies (described as separate by the Amsterdam model) to be compatible with each other. An analysis of degree adverbs (like 'hardly, barely, extremely') in Spanish is conducted with the aim of showing the benefits of such a new theory. This theory accounts indeed for the fact that a quantifier may carry out more than one function, due to the different degree of categorial flexibility of quantifiers.

Flexibility of PoS is also the topic of the following contribution, by J. Rijkhoff, ''On flexible and rigid nouns,'' whose central claim is that ''nouns that are used cross-linguistically to refer to a single, concrete object can be divided into flexible and rigid subtypes'' (p. 227). From a semantic point of view, flexible nouns are characterized by the fact of being vague so that category assignment is established in phrasal context. By using a representative sample of the world's languages, Rijkhoff describes a set of nouns according to the categories of Shape and Homogeneity, which are, in his terminology, the features of nominal Seinsart , i.e. 'kind of being' (vs., verbal Aktionsart). These features are shown to correlate with important grammatical phenomena such as number agreement. Furthermore the author displays how the distinction between rigid and flexible nouns also plays a role in the PoS hierarchy: Verb > Noun > Adjective > (manner) Adverb (Hengeveld 1992).

However the distinction between rigid and flexible PoS -- already well acknowledged by Hengeveld et al. (2004) -- is further investigated by K. Hengeveld himself and E. van Lier in their contribution ''Parts of speech and dependent clauses in Functional Discourse Grammar.'' On the basis of a sample of 23 languages, the authors adopt the theory of Functional Discourse Grammar in order to show that PoS and dependent clauses constructions can both be described by their functions in a comparable way. After introducing the Functional Discourse Grammar formalism and placing PoS in this model, Hengeveld and van Lier show dependent clauses to be functionally defined in the same way as PoS -- certainly, in this case, complex clausal units substitute PoS lexical units. The last part of the article analyses how flexible and rigid PoS systems correlate with morpho-syntactic function-marking.

EVALUATION The common thread of this volume, as expressed in the title, is typological research on PoS in which empirical methods are well anchored to a clear theoretical apparatus. My evaluation of the volume is strongly positive. Besides the very high quality of every contribution, I particularly appreciated the continuity of the discussion in which the assorted parts fit well together: every essay is functional to and helps a better comprehension of the others. Even the order in which the papers have been presented helps the reader to follow the thread of discussion, despite the differences of topics and theoretical frameworks of the papers. Many research fields are brought together: (stricto sensu) theoretical linguistics, research on sign languages, language acquisition, pragmatics, language contact, diachrony. All these perspectives are linked together by common typological interests that characterize each contribution of the book.

Many of the contributions are reports on research that is still in progress. However, they offer useful cues on future research about specific word classes and above all they are examples of theoretical and methodological rigour. For instance, Lehmann's discussion of levels of categorization offers a key for looking cross-linguistically at the concept of root, avoiding misunderstandings that often happen when one tries to have different research frameworks interact (see e.g. Civilleri, forthcoming). Some frameworks (e.g., generative grammar) claim the root to be pre-categorial, whereas others (e.g., classic comparative linguistics) consider the root as meaningful and categorised. Thus, one should be aware that the same term may encode two different concepts. In the existing literature about PoS, the book remarkably tries to go beyond the differences among research fields and perspectives by emphasizing the guidelines that should inspire all of them. The importance of empirical investigation is underlined by many authors and each of them also shows the way in which scholars should ground their research on a firm theoretical basis. Such a theoretical solidity is crucial for any methodology of analyzing linguistic data.

Germana Olga Civilleri graduated in Classics at the University of Palermo. She received her PhD in Linguistics at Roma Tre University with a dissertation on deverbal nouns in Ancient Greek. Her research interests are Classical languages, historical linguistics, case systems, the noun-verb continuum, deverbal nouns, and word formation and the lexicon.